Environmental Engineering Reference
In-Depth Information
patterns may be strongly influenced by surface floods and ground-water levels (Zimmermann, 1969;
Friedman et al., 1996b).
Fig. 2.51 Distribution of typical riparian plant communities in relation to fluvial landforms. Idealized individual
species distributions are shown in bars A through H; for example, species A typically grows on floodplains and
terraces and is restricted on lower fluvial surfaces (after Hupp, 1992)
The following descriptions and definitions (from Hupp and Osterkamp, 1996) are for the typical fluvial
landforms found along most streams from temperate to semi-arid regions. The term bottomland refers to
all fluvial generated landforms and the vegetation they support. These landforms occur as terraces high
in the valley section and, in descending order, proceed through floodplain, various riparian features
including riverine wetlands, channel bars, to the channel bed (Fig. 2.51). Alluvial streams impacted by
channel incision will be dominated by fluvial processes during the recovery period. The recovery process
(unaided by human restoration) may require decades to centuries (Hupp, 1992).
Table 2.3 Fluvial-landforms and their relations with vegetation type, flow duration (i.e., percentage of time the
l andforms are inundated), and flood frequency (Hupp and Osterkamp, 1996)
Fluvial landform
Vegetation type
Flow duration
Flood frequency
Channel bar
Largely absent
About 40%
Channel shelf
Riparian shrubs
5%-25%
Floodplain
Floodplain forest
1-3 years
Terrace
Terrace assemblage
>3 years
The channel bed is the surface that is wholly or partly covered by flows below mean annual discharge.
Thus, at least part of the channel bed is inundated at all times. Channel bars (Fig. 2.51, Table 2.3) occur
in the active-channel part of the valley section and are the lowest prominent geomorphic feature higher
than, but within, the active-channel bed. The level of the channel bar generally corresponds to a stage
slightly higher than the low-flow water stage. The channel shelf, a bank feature, is a horizontal to gently
sloping surface (Fig. 2.51, Table 2.3). The channel shelf is best developed along relatively steep-gradient
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